A British newspaper says British military scientists tested a chemical weapon on Indian colonial troops during more than a decade of experiments before and during World War Two.

The Guardian newspaper report published Saturday says hundreds of Indian and British soldiers were exposed to mustard gas in tests conducted in Rawalpindi, which was then part of Britain's Indian colony, and is now in Pakistan.

The Guardian says its report is based on documents discovered in Britain's National Archives.

The documents reported to say that the gas severely burned the soldiers' skin, and caused pain that sometimes lasted for weeks. Some of the soldiers had to be hospitalized.

The newspaper alleges no attempt was made to measure long-term effects of exposure to the gas.

The British Ministry of Defense has not said if the Indian soldiers were volunteers.

The documents allegedly indicate the scientists wanted to compare the effect of the gas on the skin of Indians to the results of experiments done on British soldiers.

The Guardian says the British scientists were developing poison gases for use against Japanese troops.

The scientists worked for Porton Down, the world's oldest chemical warfare research installation.

Britain's Ministry of Defense says at least 20,000 British soldiers took part in chemical warfare trials between the time facility opened in 1916 and 1989.